the fall of a meteor over russia became an internet sensation. the object is believed to be around 50 feet wide and 10,000 tons when it entered the earth's atmosphere injured some 1,200 people when it slammed into earth. the meteor was a surprise, even more so because it came just hours before another cosmic event. later the same day, an asteroid passed about 17,000 miles from earth, closer than some satellites. the astronaut was expected, but it hadn't been on nasa's radar, until its discovery by an observatory in spain a couple years before. these two objects have put a new spotlight on objects that pose a risk to earth on any given day. most burns up or is so small we don't know it. nasa is aware of some 20,000 pieces of debris that are currently orbiting the earth that are the size of a softball or large. but the real concern is around neos or near earth objects or asteroids that could conceivably enter our atmosphere. 863 are asteroids with a diameter roughly half a mile or larger, which if they struck earth, could produce a major global cat